In a system comprising several data processors, each processor must be loaded with an initial program in an operation referred to as Initial Program Load IPL when the system is switched on, or after a power failure.
If the data processors are located remote from each other, an operator would have to be available at each station where an initial program load is required. As in many applications, at least some of the processors in a distributed system could be left unattended most of the time, it would be desirable to have a possibility for remotely initializing processors when the necessity arises, and to utilize the available communication means for this purpose.
In the prior art, some possibilities for initializing a station or processor prior to its operation are described, or basically indicated.
U.S. Pat. No. 4,051,326 to Badagnani discloses an arrangement for remote switching-on and initialization of a data terminal. In this system, a simple ring signal from a remote computer triggers the switching-on of the terminal and the loading of an initialization program which is already available in a peripheral unit of the terminal. A ready signal is returned when the initialization is completed.
In U.S. Pat. No. 4,030,073 to Armstrong, a computer system is described comprising a circuit which, upon turning-on or reenergization of the power supply, transmits address signals which divert the computer to an initialization routine permanently stored in the circuit. This routine includes computer instruction sequences for performing preliminary diagnostic operations and for transferring instructions to main memory from preselected peripherals.
Though both of these systems disclose arrangements for initializing a device automatically under certain conditions, the respective data must be previously available within the station or computer unit which is to be initialized. They both do not provide for the complete remote loading of an initialization program from one computer into another over equal stations which attach the computers in a peer-to-peer fashion to a communication facility interconnecting them. They also do not disclose the automatic requesting, by a computer communication station, of initialization data from a remote device when required.
The Manual "IBM Synchronous Data Link Control--General Information", Form No. GA 27-3093-0 (published March 1974) suggests principles for communication systems in which information is exchanged between stations in the form of formatted frames. Two frame types are proposed for initialization: A Request for Initialization frame which is transmitted by a secondary station to notify the primary station of the need for being set into initialization mode, and a Set Initialization Mode frame which initiates system-specified procedures at the receiving secondary station, for the purpose of initializing link-level functions. An acknowledgement frame is the expected response.
Though the suggested frames are suitable for an information exchange between two stations, there are following limitations: The intended system has a fixed primary station and a number of secondary stations, and no initialization in a system with equal peer-type stations is proposed; the initialization is only for link-level functions, and no complete processor initialization from another processor is involved; and the suggested frames only cover two initial steps while detailed procedures for full initialization are not disclosed but are intentionally left to the respective system in which the two frame types are implemented.
A two-step procedure for transmitting data between a central processor and peripheral devices is disclosed in U.S. Pat. No. 3,909,782 to Mazier. Though the described method and device are suited for controlling the transfer of preparatory information and the transfer of the data proper between two functional units, they do not disclose the exchange of program information between equal stations for initializing one from the other.
One object of the present invention is to provide, in a multi-station communication system interconnecting a plurality of processors, a method and means for loading an initial program stored in one of the processors, into another processor.
Another object is to provide such a system in which any one of the stations can be given the status of an IPL Source station to which the processor holding the IPL data is attached, while any other station can be given the status of acceptor station which can request and accept IPL data for its attached processor from a remote processor.
A further object is to provide a communication system for a plurality of independent processors with provisions for remote initial program loading, in which any station having a processor attached to it that needs IPL data will automatically generate and transmit a request for remote IPL.
Another object of the present invention is a multi-station processor intercommunication system in which for the purpose of remote IPL from a selected source, a station can be given two different acceptor states, so that in one state it must automatically accept an IPL data sequence from a source at any time, while in the other state it can, after a first IPL, select to refuse another IPL data sequence.
These and other objects and advantages of the invention will become more apparent from the following description in which a preferred embodiment is disclosed in connection with drawings.